On 27 June 1997 at 0439 a strong earthquake struck the Azores Archipelago. This main shock reached M 5.5 and was felt with maximum intensity of V on the Modified Mercalli Scale at Terceira and São Miguel islands; in the islands of São Jorge, Pico, and Faial, the respective maximum intensities were III/IV, III/IV, and II/III.

The epicenter was in the vicinity of Don João de Castro bank (figure 2), a submarine volcanic structure. An earthquake swarm began the same day. During one month about 2,000 such events were registered at a reference seismic station on São Miguel island. Approximately 45 earthquakes with M >4 were registered at Terceira island. By 12 September about 2,100 earthquakes had occurred but by then the swarm had declined to 1 or 2 small events a day.

Figure 2. Epicenters during part of the seismic swarm at the Don João de Castro bank (Azores Archipelago), 27 June to 2 August 1997. Provided by SIVISA; courtesy of J.L. Gaspar.

In 1720 AD the Don João de Castro Bank produced an eruption with a Volcanic Explosivity Index (VEI) of 3. After four days an ephemeral, 1-km-long island was created. The area was charted in 1941. Seismic swarms in this general region were also noted in 1988 and 1989 (SEAN 13:10 and 14:03).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

[Don João de Castro Bank information only; extracted from a summary of significant seismic activity in the E Azores since May 1988.]

"A small swarm of earthquakes occurred within the volcano Don João de Castro Bank (figure 1, zone 4) 3-5 October. Sixty-two earthquakes were recorded; no harmonic tremor was detected. A felt earthquake occurred in the same area 23 October; it had intensities of MM IV-V on Terceira and MM III-IV on the N coast of Sao Miguel."

Figure 1. Sketch map showing islands in the eastern Azores. Approximate epicenters of the 3-5 October 1988 swarm at the submarine volcano Don Joao de Castro Bank (4) and the 21 November 1988 and 21 January 1989 earthquakes in the Hirondelle Basin (6 and 7) are shown. Courtesy of R. Moore.

On 27 June 1997 at 0439 a strong earthquake struck the Azores Archipelago. This main shock reached M 5.5 and was felt with maximum intensity of V on the Modified Mercalli Scale at Terceira and São Miguel islands; in the islands of São Jorge, Pico, and Faial, the respective maximum intensities were III/IV, III/IV, and II/III.

The epicenter was in the vicinity of Don João de Castro bank (figure 2), a submarine volcanic structure. An earthquake swarm began the same day. During one month about 2,000 such events were registered at a reference seismic station on São Miguel island. Approximately 45 earthquakes with M >4 were registered at Terceira island. By 12 September about 2,100 earthquakes had occurred but by then the swarm had declined to 1 or 2 small events a day.

Figure 2. Epicenters during part of the seismic swarm at the Don João de Castro bank (Azores Archipelago), 27 June to 2 August 1997. Provided by SIVISA; courtesy of J.L. Gaspar.

In 1720 AD the Don João de Castro Bank produced an eruption with a Volcanic Explosivity Index (VEI) of 3. After four days an ephemeral, 1-km-long island was created. The area was charted in 1941. Seismic swarms in this general region were also noted in 1988 and 1989 (SEAN 13:10 and 14:03).

Volcano Types

Submarine

Tectonic Setting

Rift zoneOceanic crust (< 15 km)

Rock Types

Major
Basalt / Picro-Basalt

Population

Within 5 kmWithin 10 kmWithin 30 kmWithin 100 km

0
0
0
116,504

Geological Summary

Don Joao de Castro Bank is a large submarine volcano that rises to within 13 m of the sea surface roughly halfway between Terceira and San Miguel Islands. Pillow lavas form the base of the volcano, which is capped by basaltic hyaloclastites. A submarine eruption during December 1720 produced an ephemeral island that attained a length of 1.5 km and an altitude of about 250 m before it was eroded beneath the sea surface two years later. The volcano (also spelled Dom Joao de Castro) was named after the Portuguese hydrographic survey vessel that surveyed the bank in 1941. Two youthful parasitic craters, one tephra covered and the other sediment free, are located on the NW flank. The submarine volcano has an impressive shallow fumarole field and remains seismically active.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Dom Joao de Castro Bank | Castro Bank

Photo Gallery

Two unusual-looking flank craters are visible in this side-viewing sonar perspective of the NW flank of Don Joao de Castro Bank in the Azores taken by U.S. Navy submarine NR-1. The two craters are 90 x 45 m wide. The left-hand and younger crater displays a floor consisting of a chilled lava lake with polygonal surface fractures. The right-hand crater is much less distinct because its surface is obscured by tephra deposits. The line at the right is the center track line of the sonar image.

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).